In wireless communication systems there is a constant strive for improvement of transmission technologies in order to utilize the available spectrum in most efficient way. Various standards using different radio access technologies have been introduced, one of which is 3GPP LTE (Long Term Evolution). LTE supports high data rates and low latency both for uplink traffic as well as for downlink traffic.
An advantage of an LTE system is the possibility to tailor the modulation and coding scheme (MSC) of the transmissions. In particular, link adaptation is used and based on Channel State Information (CSI), e.g. based on measured instantaneous Signal to Interference and Noise Ratio (SINR) at a wireless device. The wireless device uses the SINR for indicating its recommended modulation and coding scheme for use in subsequent transmissions.
However, channel conditions often change faster than the feedback system in LTE is able to communicate the changes. Thus, sub-optimal modulation and coding may be chosen; i.e. lower modulation and code rate are chosen than the instantaneous channel could support, leading to lower performance than what would actually be possible.
Another feature of LTE is Multi-User Multiple-Input-Multiple-Output (MU-MIMO). The gain and benefits of using MU-MIMO is to a large extent dependent on the ability of pairing the users in a careful way. This can be predicted to some extent, but in order to obtain the full potential of MU-MIMO the correct modulation and coding for a specific pairing of users should be chosen. The co-scheduling of users is therefore highly dependent on the accuracy of the feedback from the wireless devices.
Accurate feedback from wireless devices is thus important for various situations and aspects.
Channel selection is a known way of transmitting feedback information in LTE. It has also been suggested that channel selection is used for transmitting CSI on the Physical Uplink Control Channel (PUCCH).